Heidi Klum maintains her fit bikini body despite being the mom of four small children. (Photos: SI/Instagram, Celebrity Health Fitness)

Ludwig said the real cause of weight gain isn’t too many calories, but a diet that’s high in refined carbs and sugars. This is because our body stores fat when we experience insulin spikes, which are caused by eating too much sugar and processed grains like white bread, he explained.

Heidi also tries to work out every day combining circuit-training workouts, strength-training, lunges, step-ups and rows, as well as belly-targeting exercises to keep her abs flat.

Klum makes an effort to incorporate exercise into her daily life by hiking with her children when they’re in Los Angeles, running on the treadmill for 30 minutes at home, and doing sit-ups and other calisthenics in her hotel room whenever she travels.

Heidi Klum says she has never had plastic surgery and has no plans to. (Photo: Instagram, Celebrity Health Fitness)

While most people dread getting older, Heidi is comfortable with aging and has no interest in getting plastic surgery.

“I don’t think of getting older as looking better or worse; it’s just different,” said Klum. “You change, and that’s OK. Life is about change.”